Several types of tunable capacitors have been used in electronics. These include physically tuned capacitors where the plates of the capacitor are moved relative to each other to change the amount of effective area of the plates, or the distance between the plates, to thereby change the capacitance of the capacitor. These types of capacitors can have a large amount of variance in their capacitance, but they require an actuator to be controlled automatically. Other tunable capacitors include those that use electrically active materials that have a dielectric constant that can be changed by applying an electric field through the material. These materials are either ferroelectric (f-e) or paraelectric (p-e). While the dielectric constant of these materials can be change relatively quickly, the change in capacitance with a voltage applied is rather small.
Electrical, radio frequency (RF), or microwave applications of these tunable capacitors include such general classifications as varactor diode replacement, tunable filters, phase shifters, multiplexers (to include duplexers), voltage controlled oscillators, tunable matching networks for power amplifiers (PA's), low noise amplifiers (LNA's), thermoelectric effects including power systems, general impedance matching networks, and charge pumps.
Tunable capacitors can be exploited in the design of components, subsystems and/or systems in mobile communication systems to achieve:                1) new capability and improved electrical (RF or microwave) performance over a wide range of frequencies but most particularly from 300 MHz to ˜30 GHz        2) smaller size,        3) lower power consumption,        4) less weight,or any combination of these four items as determined by specific system design requirements.        
Electronics, including wireless handsets are characterized by their need for low voltage operation, typically <40 VDC, and ideally <3.0 VDC. It is expected that this voltage will decrease further in future designs. Thus, any tunable device must be able to be designed in such a way as to create appropriate electric fields from a small DC power supply voltage. One way to achieve a suitable geometry is to design variable capacitors consisting of thin films of f-e materials, with closely spaced biasing electrodes. The small DC tuning voltage also results in reduced power consumption (and heat dissipated) from RF and E-O devices. Another use of tunable capacitors to achieve the tunability required is to provide a higher tuning voltage from a low voltage source using charge pumps. This is done conventionally by charging a number of capacitors in parallel and them switching them to a series configuration, to add the voltages together. These techniques provide tunable capacitors, while avoiding the limitations of f-e materials.
Another use of interest for the capacitors of the present invention, is pressure or temperature sensors. Changes in temperature/pressure affect many applications and smaller temperature/pressure sensors are always in need in a wide range of industries that include hydraulic and pneumatic systems. Currently these work on a number of principles including the movement of one capacitor electrode relative to another electrode. The relative movement between electrodes causes a change in capacitance which results in a change in an electrical signal that is used to detect and/or direct the operation of systems. The higher the capacitance change the more sensitive the feedback of data and the greater the accuracy of system control.